The invention relates generally to fiber optic sensors, and more particularly to the structure, including the fiber optic clad, in a modular fiber optic sensor.
Fiber optic sensors utilize the transmission properties of an optical fiber, which is a function of the refractive indexes of the core and the clad. For good transmission of light through the fiber, the index of the clad must be lower than the index of the core. The typical fiber optic sensor places a specific chemistry reaction system at the tip of a standard fiber. The tip is exposed to the sampling environment and the fiber is used to transmit an excitation signal and/or a response signal. Sensors have been made by placing the reaction chemistry along the side of a fiber core to enhance its signal. U.S. patent application Ser. No. 046,986 filed May 6, 1987 teaches the formation of a fiber optic sensor in which the reactive material forms the clad itself, or alternatively is sandwiched between the core and the clad in cases where the reactive material is unsuitable or undesirable for the clad. In the sandwich configuration, the clad must be porous, with holes of the right size to allow the desired species to contact the reactive layer. In such cases it is difficult to form a good clad layer. In all of those configurations, the measurements are made with the sensor in-situ. It is desireable to have a simple and widely applicable method for forming a clad on a fiber optic sensor in order to provide maximum interaction between the active surface and the analyte. It is also desireable to have a modular sensor configuration which allows measurements to be made after the sensor is removed from the sampling environment.